In gas chromatography, a liquid sample is injected into a gaseous system, maintained under elevated pressure (e.g. 20 psi), where it undergoes analysis in accordance with well known procedures. To simplify injection of the sample material into the pressurized system, the equipment is provided with injection ports sealed by an elastomeric septum. Injection needles are utilized to penetrate the septum and to inject the sample material into the pressurized ambient, after which the needles are withdrawn and the system is automatically resealed by nature of the elastomeric septum's self-sealing properties.
In practice, the injection ports are penetrated multiple times by injection needles over the course of time, until the septum becomes degraded by tearing and coring, which causes the system to not function properly. At this stage, the septum must be replaced, requiring the instrument to be temporarily taken out of service.
With known systems, multiple penetration of a septum typically causes it to become torn and ragged in the penetrated area, and in many instances to be cored by the injection needle. When this occurs, small bits of the septum material can enter the pressurized gas stream of the chromatograph. The chromatograph then senses the presence of the foreign material and delivers a read-out that is at least partially in error as a function of sensing the foreign material along with the material of the test specimen.